Structural Neuroimaging: From Macroscopic to Microscopic Scales

Abstract

This chapter discusses structural MRI (sMRI) techniques to image the brain anatomy, with a focus on diffusion MRI (dMRI). Conventional sMRI, including T1-, T2-, T2*-weighted MRI, gives rich contrasts to delineate the brain structures and provides important information about the structural volume, shape, and relaxometry. Compared to conventional relaxation-based contrast mechanisms, the dMRI technique offers unique contrasts based on translational molecular motions, which are restricted by microstructural barriers such as cell membranes and axons. We will describe the essential components of a dMRI pulse sequence, including the various diffusion encoding schemes and image acquisition techniques to achieve high-resolution dMRI. We will then introduce biophysical models that reconstruct the microstructural information (cell size, density, permeability, axon diameter, etc.), using dMRI signals acquired with different diffusion directions and weighting strength (q-space) and different diffusion times. In the end, a few exemplary clinical and preclinical applications of dMRI will be reviewed, and the current challenges and potential future directions will be discussed.